1. Field of the Invention
The present disclosure relates to an electrostatic charge developing toner, electrostatic charge developing developer, and image forming apparatus that are used in an electrophotographic system.
2. Description of the Related Art
In an electrophotographic image forming apparatus for forming an image on a sheet, such as a copier, a printer, or a digital multi-functional peripheral, an electrostatic image (electrostatic latent image) is formed on a circumferential surface of a photoreceptor drum serving as an image carrier, and is then developed into a toner image by a developing device using a toner. The toner image on the photoreceptor drum is transferred to a sheet by a transfer device, and then heated, pressurized, and fixed to the sheet by a fixing device. The sheet having the toner image fixed thereto is eventually discharged to the outside of the image forming apparatus.
Deformed resin fine particles are fixed to the surfaces of toner particles of the toner used in the above-described electrophotographic system in recent years, in order to prevent the resin fine particles from adhering to a developing sleeve or photoreceptor drum and stabilize image quality over a long period of time.
In order to cope with toner fixation at low temperatures and increasing the image quality resulting from increased speeds and energy saving of digital multi-functional peripherals and printers, a toner used in an electrophotographic process is gradually reduced in diameter and consequently subjected to thermal stress and physical stress, easily changing the state of the toner (change in shape of the toner and how an external additive is buried). This change in state causes a change in the performance of each process, narrowing the design margins and causing other troubles. Therefore, it is important to control such change in state in order to maintain image quality.
The greatest impact of the change in state causes fogging and scattering of the toner due to defective charging of the toner, which is caused when replenished toner having high electrostatic chargeability is mixed with a toner having low electrostatic chargeability that is generated when inorganic fine particles as the external additive are buried in toner base particles when mixing a developer.
For this reason, the resin fine particles are added in order to prevent the occurrence of the defective charging. This is because the resin fine particles, unlike the inorganic fine particles, are effective in preventing the defective charging by its similarity in charging system with a binder resin of the toner. Particularly, although the resin fine particles have low positive charging characteristics in the beginning when being mixed with a carrier, the positive charging characteristics gradually increase, and consequently the resin fine particles prevent a change in charging caused by the inorganic fine particles and effectively preventing the occurrence of fogging or scattering during images are formed.
An electrostatic charge developing toner has been reported as the toner having the resin fine particles fixed to the surface thereof. Organic fine particles with a number average particle diameter which is at least 50 nm but less than or equal to 200 nm and a variation of shape coefficient SF-1 equal to or lower than 10% before and after a forcible stirring test, are externally added to the toner. The glass-transition temperature of this toner is at least 20° C. but less than or equal to 45° C.
The known conventional technology described above, however, exerts a spacer effect by fixing special hard resin fine particles, not deformed, to a toner surface to ensure stable fixation performance or transfer performance. Adding the resin fine particles is not to prevent defective charging.
In addition, the specific gravity of the resin fine particles is normally approximately 1 to 1.2 g/cm3, which is too low to fix the resin fine particles to the toner surface. Consequently, the resin fine particles easily separate from the toner surface. Due to the low hardness of the resin fine particles, the resin fine particles are deformed easily and adhere to the carrier, developing sleeve, photoreceptor drum and other toner carriers, causing a defective image.
The present disclosure was contrived in view of the circumstances described above, and an object thereof is to provide a toner in which resin fine particles are fixed to a toner surface such that the resin fine particles are deformed when added thereto, and in which defective charging and toner carrier contamination are prevented by controlling the level of deformation.